论文标题
考虑声子自由能对磁状态的依赖性的居里温度的预测
Prediction of the Curie temperature considering the dependence of the phonon free energy on magnetic states
论文作者
论文摘要
居里温度的预测对于铁磁材料的设计至关重要。即使使用海森贝格模型估算了居里温度，但磁性交换耦合参数却广泛使用的是基于零温度下的第一原理计算。在明确考虑温度效应的情况下，重要的是要最大程度地减少总自由能，因为磁子和声子自由能相互关联。在这里，我们提出了一种第一原理热力学方法，以最大程度地降低磁子对声子的影响以及从声子到磁性的反馈效果的总自由能。通过将我们的方案应用于BCC FE，我们发现由于反馈效应，库里温度大大降低。这一结果不可避免地会强制我们改变惯例，如下所示：在预测居里温度时，我们应该将交换耦合常数用于无序的局部力矩状态，而不是针对铁磁状态。我们的结果不仅改变了对有限温度磁性的基本理解，而且还提供了一个通用框架，以更准确地预测居里温度。
Prediction of the Curie temperature is of significant importance for the design of ferromagnetic materials. Even though the Curie temperature has been estimated using the Heisenberg model, magnetic exchange coupling parameters widely used is thus far based on first-principles calculations at zero temperature. In the explicit consideration of temperature effects, it is important to minimise the total free energy, because the magnetic and phonon free energies correlate with each other. Here, we propose a first-principles thermodynamic approach to minimise the total free energy considering both the influences of magnetism on phonons and the feedback effect from phonons to magnetism. By applying our scheme to bcc Fe, we find a significant reduction of the Curie temperature due to the feedback effect. This result inevitably enforces us to change our convention as follows: we should use exchange coupling constants for the disordered local moment state, not for the ferromagnetic state, in the prediction of the Curie temperature. Our results not only change the fundamental understanding of finite-temperature magnetism but also provide a general framework to predict the Curie temperature more accurately.
